1. Field of the Invention
The invention concerns a method for recognition of direction of rotation for the ignition system of an internal combustion engine using a magnet wheel which can be moved past an electrical ignition coil arrangement by the internal combustion engine. As a result, there is induced in the coil arrangement, for each revolution, at least one current pulse or voltage pulse whose polarity is dependent on the direction of rotation. The invention further concerns an ignition module with (electronic) evaluation means for recognition of direction of rotation according to the aforementioned method. In this case, the evaluation means perform sampling, evaluation and/or processing of current pulses or voltage pulses which have been induced by interaction with the rotating magnet wheel. The invention further concerns a direction of rotation detector, suitable for use in the said method or ignition module, whose input can be coupled to an alternating voltage source, in particular, to an ignition coil arrangement excited by a magnetic alternating field, for the purpose of sampling, evaluating and/of filtering current half-waves or voltage half-waves generated therein.
2. Description of the Related Art
Ignition systems with recognition of direction of rotation are used in hand-controlled working equipment with an internal combustion engine in which no ignition sparks are to be generated when the engine is running backwards. This is because, on starting, such internal combustion engines have a tendency to xe2x80x9coscillatexe2x80x9d contrary to the direction of rotation, due to high compression pressures. In order that the engine does not start in the backward direction, however, an objective to be sought is that the ignition module does not emit any ignition sparks upon backward rotation (cf. U.S. Pat. No. 5,606,958).
Known in the art (cf. U.S. Pat. No. 5,050,553) is the practice of evaluating by means of control electronics the sequence of voltage half-waves induced in each revolution of the internal combustion engine, or the magnet wheel driven by it. These control electronics operate with displacement curves for the starting ignition and the operating ignition. These two curves overlap one another over a rotational speed range which has the idling rotational speed as the upper limit. The control requirement for interrogating and differentiating these two curves is considerable. In order to permit reliable recognition, it is necessary to take into account a large angular range, which reduces the reaction time and dynamic response.
A known ignition system for an internal combustion engine (U.S. Pat. No. 5,606,958) is provided with an additional winding on a separate I-shaped iron core. During the normal rotation of the magnet wheel, this additional winding is first passed by the magnet poles before the poles move past two limbs of a further, subsequent magnetic iron core. The voltage induced in the additional winding is used to suppress trigger pulses in respect of a switching device when the engine is rotating backwards. A disadvantage is that a separate core is required for the additional winding and, as a consequence, additional construction space. Moreover, the additional winding must be contacted with the electronics printed circuit board.
Known from DE-A-37 06 725 is an ignition device with permanent magnets, guided past iron core limbs, with two pole shoe magnets. In order to increase the security against backward rotation, the pole shoe packet following in the operating direction of rotation is designed to be of such a length that, in running past, it magnetically short-circuits the iron core limbs of the ignition coils. This, however, results in an asymmetrical design of the pole shoes of the magnet wheel. The increased production and material requirement which results is obvious.
A generic capacitor ignition system is known from DE-A-36 08 740. In order to protect the internal combustion engine operated by it against running backwards, a direction of rotation detector is provided which is intended to prevent the discharge of ignition pulses in the event of an incorrect direction of rotation of the engine. To realize this, electronics are proposed for ascertaining the number of positive and negative half-waves induced in a magnet generator. This is because, in the case of the usual construction of generic magnet generators with a U-shaped iron core and coils disposed on at least one of the limbs of this core, depending on the direction of rotation of the magnet wheel provided with the permanent magnets, there is produced in the coil an induced voltage which consists either of two negative half-waves and one positive half-wave, or of two positive half-waves and one negative half-wave. The electronics can thus ascertain the number of positive and/or negative half-waves and, consequently, the direction of rotation of the magnet wheel. In this case, however, there is a need for pulse counting together with preceding rectification over a relatively large angular range, resulting in an increased counting time and a reduced dynamic response. The information, or indication, of the direction of rotation is only available at the end of a period with the half-wave sequence.
The object of the invention is to create a direction of rotation recognition system, suitable for an internal combustion ignition system, which renders possible ascertainment of the direction of rotation with a minimal angular range with a greater speed and dynamic response and a reduced circuitry and/or programming requirement. In particular, the result of the recognition of the direction of rotation is to be fixed in respect of angle, i.e., always available in the same rotational position of the magnet wheel.
Proposed to achieve the object are the method disclosed in claim 1, the ignition module disclosed in claim 7 and the direction of rotation detector disclosed in claim 18. Advantageous developments are given by the dependent claims.
Within the scope of the general inventive concept, a voltage signal point which is indicative of the direction of rotation of the magnet wheel is used in the voltage signal of a coil disposed on an expediently U- or E-shaped iron core. For this purpose, the voltage signal is shaped or modified in such a way that it contains a feature which is indicative of the direction of rotation. According to the invention, therefore, a method and electronics for its implementation are developed which provide the information on the direction of rotation in the form of an indicating signal. This can be suitable for controlling the trigger electronics in the ignition module in such a way that an ignition pulse or ignition operation is initiated only in the case of forward rotation.
For the purpose of realizing the indicative point in the voltage signal, use is made, according to the invention, of a magnet pole arrangement, or pole shoe arrangement, and a coil arrangement which have such geometric relationships to one another that, upon each magnet wheel revolution, at least one discontinuity point, in particular, a break point or, also, a region or section with two or more extreme points (maxima, minima) occur in the curve characteristic of a voltage half-wave of determined polarity. The physical conditions and relationships for generating the indicative points such as discontinuity points, break points, extreme points or dips in the voltage signal of an ignition coil are known to the specialist in the art (cf. patent publications U.S. Pat. Nos. 3,722,488, 3,809,040, 4,074,669 and IT-A-1 235 393 and magnet wheel ignition module arrangements available on the market). Hitherto, however, these known relationships have not been generated or used specifically for the purpose of recognizing direction of rotation. Such a curve characteristic can then be xe2x80x9cconsultedxe2x80x9d in respect of polarity and the extreme or discontinuity points with relatively simple electronics and/or software expenditure. Suitable for this purpose are electronic evaluation means, provided with a differentiating device, which can output the direction of rotation result in the form of a short pulse or also as a flag.
The invention offers the advantageous development that a voltage signal of a coil on the U- or E-shaped iron core of the ignition system can be used for the purpose of deriving the direction of rotation signal. Separate construction space, or other additional constructional measures for a separate iron core, are no longer necessary.
Since, according to the invention, the predefined polarity of the voltage pulse is ascertained by means of the discontinuity point, for example, an amplitude level dip, and the polarity reverses in known manner upon reversal of the direction of rotation, the concept of the invention makes provision whereby the direction of rotation signal is set and/or output (fixed in respect of angle) by the appropriately controlled output signal generator only upon forward rotation of the magnet wheel.
For the purpose of realizing a minimum and/or maximum rotational speed for the internal combustion engine, provision is made, according to an advantageous development of the invention, whereby the electronic evaluation means of the ignition module comprise one or more threshold-value decision elements which respond to a predetermined signal level or amplitude value of the current pulse or voltage pulse from the ignition coil arrangement. In dependence on this, the differentiating device and/or the output signal generator is/are put into operation, supplied with current and/or activated. In this case, use is made of the fact that the signal level or the amplitude of the current pulse or voltage pulse from the coil or coils is proportional to the rotational speed of the magnet wheel, or of the internal combustion engine.
In particular, the inventive concept consists in recognition of the direction of rotation from the voltage characteristic within a half-wave or a voltage pulse on the basis of the indicative point such as, for example, dip, minimum in the amplitude peak range or other discontinuity points. Ignition coil arrangements with a U-shaped iron core whose two limbs are directed towards the circumference of the magnet wheel are used in many cases. For each revolution, this generates a voltage pulse with three half-waves of alternating polarity. According to an advantageous development of the invention, in the case of an ignition coil arrangement with a U-shaped iron core, the middle half-wave is used to contain the information on the direction of rotation in the form of the indicative discontinuity point or extreme point, including a voltage dip. The preceding and succeeding voltage half-waves of opposite polarity can therefore be removed, in particular, filtered out, by the evaluation means, so that the middle half-wave can be evaluated independently of the preceding or the succeeding half-wave. This achieves the advantage that only a very small angular range, of the order of magnitude of one degree, need be evaluated for the purpose of recognition of the direction of rotation.
A further advantage of the general inventive concept consists in the fact that it can be realized by means of discrete circuit technology with a CR differentiating device and simply constructed transistor switching elements, the latter, in particular, for realization of the output signal generator. With this technology, the voltage half-wave with the indicative point (voltage dip, break point, etc.) can be advantageously utilized as a supply voltage for the active components, such as transistor switches, in the differentiating device. Since this half-wave with the information on the direction of rotation must always have a determined polarity (for correct direction of rotation), the output signal generator is consequently activated only if the direction of rotation is correct. In this way, a direction of rotation signal can be generated with high reliability and a small circuitry requirement.
However, the invention is not limited to realization by means of discrete circuit technology. The method according to the invention can also be implemented in a programmable microcontroller in the form of a software. The coil signals are then supplied to the microcontroller via appropriate analog/digital interfaces.